In some vehicle systems, exhaust gases and gases from other engine components may enter the engine intake stream during certain conditions. As these gases contain various combinations of reductants, oxidants, and diluents, it may be desirable to determine the composition and flow rate of the gases to determine how they may affect combustion and execute appropriate combustion control actions. Towards this end, one or more gas constituent sensors may be located in the intake passage of a vehicle engine to measure the presence of reductants (e.g., HC), oxidants, and diluents (e.g., CO2 and H2O) in the intake stream. However, in some vehicle systems, gases entering the intake passage upstream of the gas constituent sensor may cause a mis-read of diluents by the gas constituent sensor. Traditional solutions to account for the presence of gases biasing gas constituent sensor readings include determining the flow rate of the gases into the intake passage and using this flow rate, in conjunction with the concentration of the gas as measured by the gas constituent sensor, to determine how to correct the gas constituent sensor's measurements. Determining the flow rate of gases entering the intake passage may often be achieved using only existing sensors, e.g. sensors which are commonly present in vehicle systems such as barometric pressure (BP), compressor inlet pressure (CIP), and manifold air pressure (MAP) sensors. For example, in the case of fuel vapors purged from a fuel vapor purge system into the engine intake via a canister purge valve (CPV), the flow rate may be a function of the vacuum level where the vapors enter the intake passage and the opening amount (e.g., duty cycle) of the CPV.
However, the inventors herein have recognized that determining the flow rate of gases entering an engine intake passage in the manner described above may not be achievable in vehicle systems which incorporate ejectors to generate vacuum (e.g., vacuum used to purge the fuel vapor storage canister, to draw blowby gases from the crankcase into the intake passage, or to recirculate exhaust gases into the intake passage). For example, a suction port of an ejector may be coupled with a fuel vapor purge system, crankcase ventilation system, or exhaust gas recirculation system, instead of or in addition to the system being coupled directly with the intake passage. A motive outlet of the ejector may be coupled with the intake passage, such that the gases entering the suction port of the ejector are directed to the intake passage via the motive outlet of the ejector. In these examples, it may not be possible to calculate the flow rate of gases into the intake passage, as it may not be possible to calculate the flow rate of gases into the ejector suction port using measurements from existing pressure sensors alone. In some systems, an additional pressure sensor may be added at the ejector suction port to enable computation of the flow rate of gases into the ejector suction port, which may constitute all or part of the flow rate of gases into the intake passage (and thus the flow rate of gases at the gas constituent sensor). However, this approach may be undesirable due to the cost of adding a pressure sensor at the ejector suction port (or at each ejector suction port, in examples where more than one system incorporates an ejector to draw gases into the intake passage).
The inventors alone have recognized that the flow rate of gases entering an ejector suction port from a vehicle system may be determined without a dedicated pressure sensor at the ejector suction port by overlaying ejector flow rate characteristics with flow rate characteristics of the vehicle system. For example, in cases where the vehicle system output is arranged in series with the ejector suction port, the intersection of the vehicle system flow rate characteristic and the ejector flow rate characteristic may provide the flow rate of the gas at the ejector suction port, as well as the pressure at the ejector suction port. In examples where the vehicle system output is not arranged in series with the ejector suction port, the flow rate of the gas in paths other than the path to the suction port may be determined using traditional methods (e.g., based on data from existing pressure sensors and other known parameter values such as CPV duty cycle for a fuel vapor purge gases), and the vehicle system flow rate characteristic may be shifted based on the flow rates of the gas in paths other than the path to the suction port. The shifted characteristic and the ejector flow rate characteristic may then be overlaid, and the intersection of the characteristics may provide the flow rate of the gas at the ejector suction port, as well as the pressure at the ejector suction port. In these examples, the flow rate at the ejector suction port may then be summed with the flow rate of the gas in any other paths leading to the intake passage upstream of the gas constituent sensor, to determine the flow rate of the gas as seen by the gas constituent sensor. The controller may then determine how to compensate the measurements taken by the gas constituent sensor based on the flow rate of the gas from the vehicle system as seen by the gas constituent sensor and the concentration of the gas as inferred by the gas constituent sensor.
Thus, in one example, flow rate of a gas from a vehicle system entering an ejector suction port may be determined by a method for an engine which includes overlaying an ejector suction port flow rate vs. vacuum characteristic with a flow rate vs. vacuum characteristic of an engine system communicating with the port, and determining a flow rate of gases from the engine system based on an intersection of the characteristics. The control system may then calculate a reductant (e.g., fuel vapor) concentration of the gases from the engine system using this flow rate and a reductant concentration measurement of the total flow at a gas constituent sensor (e.g., an intake UEGO sensor) arranged downstream of the ejector outlet in an engine intake passage. In some examples, the calculated reductant concentration may then be used to determine the effect of the reductant on diluent concentration measurements of the gas constituent sensor, so as to determine an appropriate compensation for the measurements. As diluent concentration measurements may be used as a basis for exhaust gas recirculation adjustment in some systems, compensating the diluent concentration measurements may improve adjustment of exhaust gas recirculation, among other advantages.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.